Thermo-expansive microspheres, their production process and their application

ABSTRACT

The present invention provides thermo-expansive microspheres comprising thermoplastic resinous shell and a blowing agent being encapsulated in the shell, the blowing agent which is a fluorine-containing C 2-10  compound having ether linkage, being free of chlorine and bromine atoms and gasifying at a temperature not higher than the softening point of the thermoplastic resin; and also provides the production and application processes thereof. The thermo-expansive microspheres have preferably an average particle size ranging from 1 to 100 μm and a CV, or coefficient of variation, of particle size distribution being 30% or less, and a retaining ratio of blowing agent encapsulated being 90% or more. 
     The thermo-expansive microspheres have low environmental loading and superior flame-retardant or flame-resistant performance, and have particle sizes distributing in narrow ranges. Those thermo-expansive microspheres and foamed hollow microspheres are suitable for applying to fire-proof paints, flame-retardant or flame-resistant thermo-insulating materials, flame-retardant or flame-resistant lightweight fillers, and flame-retardant or flame-resistant lightweight molded products, in addition to the conventional application field.

This application is a Continuation-In-Part of copending Application No.PCT/JP04/002053 filed on Feb. 23, 2004 the entire contents of which arehereby incorporated by reference and for which priority is claimed under35 U.S.C. § 120. This application also claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 2003-96568 filed in Japan on Feb.24, 2003. The entire contents of each of the above documents is herebyincorporated by reference.

FIELD OF INVENTION

The present invention relates to thermo-expansive microspherescomprising thermoplastic resinous shell and a blowing agent encapsulatedin the shell, especially to those having superior flame retardant orflame resistant performance and particle sizes distributing in a narrowrange; and the production process and application thereof.

TECHNICAL BACKGROUND

Thermo-expansive microspheres comprising thermoplastic resinous shelland a blowing agent encapsulated in the shell are generally calledthermo-expansive microcapsules. Various processes for producingthermo-expansive microcapsules have been studied. Japanese PatentPublication Sho 42-26524 describes a general process for producingthermo-expansive microcapsules. U.S. Pat. No. 3,615,972 describes aproduction process of thermo-expansive microspheres having polymericshell formed into uniform thickness.

For producing thermo-expansive microcapsules, hydrocarbons, for example,n-butane, isobutane, isopentane and neopentane, are usually applied.Above all, isobutane and isopentane, which impart superior expandingperformance to thermo-expansive microcapsules, are used.

MATSUMOTO MICROSPHERE (produced by Matsumoto Yushi-Seiyaku Co., Ltd.), acommercially available product of thermo-expansive microcapsules,comprises thermoplastic resin, such as vinylidene chloride polymer,acrylonitrile copolymer and acrylic polymer, in which blowing agents,such as isobutane and isopentane, are encapsulated.

Thermo-expansive microcapsules comprising polymers containing aconsiderable amount of chloride are flame-retardant even they containflammable gases. However, they are hazardous because they generatechloride and hydrogen chloride gases, and further generate phosgene whenthey are ignited.

Employing a blowing agent other than flammable hydrocarbons forimparting flame resistance to thermo-expansive microcapsules has alreadybeen proposed. U.S. Pat. No. 3,615,972 discloses certainchlorofluorocarbons applicable for the purpose, though they have notbeen applied in commercial production. Chlorofluorocarbons do not impartsufficient expanding performance to thermo-expansive microcapsules, andthey have other shortages.

Flon has also been applied for various flame-resistant products owing toits unique property. Although flon gas was admitted to be inert and havebeen used for a long time, recently, as popularly known, the use of flongas has been restricted since the depletion of ozone shield became aserious problem, and applicable fluoro-compounds are being reexamined.

Actually, chlorofluorocarbon has been replaced by chloride-freealiphatic fluorocarbons or fluorohydrocarbons. Microcapsules produced ofthose chloride-free fluoro-compounds are disclosed in Japanese PatentLaid Open Hei 6-49260.

Aliphatic fluorocarbons or fluorohydrocarbons are inert indeed and havelow ozone-depleting potential. However, they cannot be applied forproducing thermo-expansive microspheres in the form of mixture withhydrocarbons of sufficient quantity for imparting high expandingperformance to thermo-expansive microspheres, because their molecules,in which hydrogen of hydrocarbon moieties was only substituted withfluorine, have poor polarity and compatibility to hydrocarbons.Application of only one aliphatic fluorocarbon or fluorohydrocarboncauses a serious problem, i.e., insufficient expanding performance ofresultant microspheres, because such fluorocarbon cannot be completelyencapsulated in thermoplastic resinous shell in polymerization reactiondue to their poor compatibility to monomers, and results in theformation of microspheres having thermo-plastic resinous shellimpregnated with the fluorocarbon.

PCT International Application nationalized and published in Japan No.2002-511900 discloses thermo-expansive hollow particles, being filledwith an expanding agent of a mixture of (a) fluoro-hydrocarbon fluid and(b) organic ester, ether or ketone. Although fluoro-hydrocarbon fluids,such as aliphatic fluorocarbons or fluorohydrocarbons, are inert andhave low ozone-depleting potential as described above, they are notpreferable because of their high global warming potential. Aliphaticfluorocarbons or fluorohydrocarbons with low fluorine-substitutiondegree are not preferable, even if they are compatible to monomers,because resultant thermo-expansive hollow particles exhibitflammability. The particle sizes of the thermo-expansive hollowparticles produced of those fluorine compounds distribute in a broadrange, for example, a distribution range with a CV or coefficient ofvariation greater than 30%, which causes difficulty in providingproducts of constant expanding performance.

In the examples 11 and 12 of the nationalized and published patentapplication, thermo-expansive hollow particles produced of (a)fluorohydrocarbon fluid, such as the mixture of1,1,1,2,3,4,4,5,5,5-decafluoropentane and perfluorohexane (PF-5060), and(b) one of organic esters, ethers and ketones, such as dimethylhexafluoroglutarate and dimethyl octafluoroadipate are described asexamples. The hollow particles have low expanding capacity and theirparticle size distributes in a broad range.

With those reasons, expansive microcapsules are not commercially andpopularly available at present.

DISCLOSURE OF INVENTION

The object of the present invention is to provide thermo-expansivemicrospheres having low environmental loading, superior flame-resistantor flame-retardant performance, and particle sizes distributing in anarrow range.

Another object of the present invention is to provide expanded hollowmicrospheres having particle sizes distributing in a narrow range and alow specific gravity.

Further object of, the present invention is to provide thermo-expansivemicrospheres and expanded hollow microspheres applicable toflame-retardant or flame-resistant thermo-insulating materials,flame-retardant or flame-resistant light-weight fillers, andflame-retardant or flame-resistant light-weight molded products.

Further object of the present invention is to provide a productionprocess of the thermo-expansive microspheres of the present invention,which have the performances mentioned above.

Further object of the present invention is to provide compositionscontaining the thermo-expansive microspheres or expanded hollowmicrospheres of the present invention.

Further object and advantages of the present invention are clearlyillustrated in the following description.

According to the present invention, the objects and advantages of thepresent invention described above are attained, first, withthermo-expansive microspheres, which are characterized by thermoplasticresinous shell and a blowing agent encapsulated in the shell, whereinthe blowing agent is a fluorine-containing C₂₋₁₀ compound having etherlinkage and containing no chlorine and bromine atoms, and gasifies at atemperature below the softening point of the thermoplastic resin.

According to the present invention, the objects and advantages of thepresent invention described above are attained, second, with expandedhollow microspheres, which are characterized by their production processwherein thermo-expansive microspheres of the present invention areheated at a temperature above the softening point of the thermoplasticresinous shell to be expanded into a volume of 10 or more of expansionratio and produced into expanded microspheres having a true specificgravity of 0.1 or less and a particle size distribution with acoefficient of variation of 30% or less.

According to the present invention, the objects and advantages of thepresent invention described above are attained, third, with theproduction process of thermo-expansive microspheres, which arecharacterized by polymerizing at least one polymerizable monomer in anaqueous dispersion in the presence of a blowing agent to producethermo-expansive microspheres, wherein the blowing agent is afluorine-containing C₂₋₁₀ compound having ether structure and containingno chlorine and bromine atoms.

BEST MODE OF EMBODIMENT

The thermo-expansive microspheres of the present invention contain afluorine-containing C₂₋₁₀, preferably C₂₋₈, compound having etherlinkage and containing no chlorine and bromine atoms as a blowing agent.Fluorine-containing compounds gasifying at a temperature below thesoftening point of the thermoplastic resinous shell of thermo-expansivemicrospheres are preferable. For example, hydrofluoroethers, such asC₃F₇OCH₃, C₄F₉OCH₃, C₄F₉OC₂H₅, and C₇F₁₅OC₂H₅, are preferable, thoughthe blowing agents are not restricted within the scope of thoseexamples. The alkyl groups in said hydrofluoroether may be either linearor branched. The preferable amount of said blowing agent ranges from 2to 85 weight percent of thermo-expansive microspheres, more preferablyfrom 15 to 60 weight percent, and the most preferably from 30 to 50weight percent.

Said blowing agents can also be composed by blending fluorine compoundshaving ether linkage with substances which are usually applied asblowing agents and gasify at a temperature below the softening point ofthe thermoplastic resinous shell of thermo-expansive microspheres, inaddition to composing the blowing agents only with fluorine compoundshaving ether linkage.

The examples of those substances are halogenides of propane, propylene,butene, normal butane, isobutane, isopentane, neopentane, normalpentane, normal hexane, isohexane, heptane, octane, petroleum ether andmethane; low-boiling-point fluids, such as tetraalkyl silane; andazodicarbonamide, which thermally decomposes and gasifies. Thosecompounds are selected according to a temperature range wherethermo-expansive microspheres are intended to be expanded. Forreflecting the property of fluorine compounds to the property ofthermo-expansive microspheres, it is preferable to control the ratio ofthe components other than fluorine-containing compounds in a blowingagent into 50 weight percent or less, more preferably 20 weight percentor less, of the whole of a blowing agent. Greater ratio offluorine-containing compounds having ether linkage in the whole of ablowing agent results in higher reflection of the property offluorine-containing compounds to the property of thermo-expansivemicrospheres, and thus enables to provide thermo-expansive microsphereshaving flame-retardant and flame-resistant performance, and to attainhigher retaining ratio of an encapsulated blowing agent before and afterthermal expansion of microspheres as describer later.

The thermoplastic resins for forming the shell of the thermo-expansivemicrospheres of the present invention comprise a polymer of a radicallypolymerizable monomer or a mixture thereof. The examples of thosemonomers are nitrile monomers, such as acrylonitrile, methacrylonitrile,α-chloro acrylonitrile, α-ethoxy acrylonitrile, and fumaronitrile;monomers containing carboxyl groups, such as acrylic acid, methacrylicacid, itaconic acid, maleic acid, fumaric acid, and citraconic acid;vinylidene chloride; vinyl acetate; (meth)acrylates, such as methyl(meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl(meth)acrylate, t-butyl (meth)acrylate, isobornyl (meth)acrylate,cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and β-carboxyethylacrylate; styrene monomers, such as styrene, α-methyl styrene, andchlorostyrene; amide monomers, such as acrylamide, substitutedacrylamide, methacrylamide, and substituted methacrylamide; and anoptional mixture thereof. Thermo-expansive microspheres with superiorheat resistance are those having thermoplastic resinous shell producedof nitrile monomers, and the mixture of acrylonitrile andmethacrylonitrile is preferable for the purpose. The preferable ratio ofnitrile monomers in thermoplastic resinous shell is 80 weight percent ormore, more preferably 90 weight percent or more. Thermoplastic resinousshell comprising less than 80 weight percent of nitrile monomers is notpreferable for heat-resistant thermo-expansive microspheres.

The examples of cross-linking agents or polymerizable monomers havingtwo or more of polymerizable double bonds to be added to said monomerswithin the scope of the present invention are, for example, aromaticdivinyl compounds, such as divinyl benzene and divinyl naphthalene, arylmethacrylate, triacrylformal, triallyl isocyanate, ethylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycoldi(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,9-nonanedioldi(meth)acrylate, 1,10-decanediol di(meth)acrylate, PEG (200)di(meth)acrylate, PEG (400) di(meth)acrylate, PEG (600)di(meth)acrylate, neopentylglycol di(meth)acrylate, 1,4-butanedioldimethacrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanedioldi(meth)acrylate, trimethylolpropane trimethacrylate, glycerindimethacrylate, dimethylol tricyclodecane diacrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetraacrylate, dipentaerythritolhexaacrylate, neopentylglycol acrylic acid benzoate, trimethylolpropaneacrylic acid benzoate, 2-hydorxy-3-acryloyloxypropyl methacrylate,hydroxypivalic acid neopentylglycol diacrylate, ditrimethylolpropanetetraacrylate, and 2-butyl-2-ethyl-1,3-propanediol diacrylate, and themixture thereof. The amount of those cross-linking agents rangespreferably from 0.01 to 5 weight percent, more preferably from 0.05 to 3weight percent of the whole of compounds to be polymerized. An amountless than 0.01 weight percent results in low degree of cross-linkingleading to poor retention of encapsulated blowing agent and poor heatresistance of resultant microspheres. An amount greater than 5 weightresults in excessive degree of cross-linking which extremelydeteriorates the expanding performance of microspheres.

Shell materials of thermo-expansive microspheres are prepared by addingproper polymerization initiators to the components described above.Polymerization initiators known to those skilled in the art, such asperoxides and azo compounds, can be employed. The examples of peroxidesare azobisisobutyronitrile, benzoyl peroxide, lauryl peroxide,diisopropyl peroxidicarbonate, and t-butyl peroxide, and the examples ofazo compounds are 2,2′-azobis (4-methoxy-2,4-dimethyl valeronitrile),2,2′-azobis isobutyronitrile, 2,2′-azobis (2,4-dimethyl valeronitrile),2,2′-azobis (2-methyl propionate), and 2,2′-azobis (2-methylbutyronitrile). Preferable polymerization initiators are oil-solubleinitiators which are soluble in polymerizable monomers employed.

For producing thermo-expansive microspheres, conventional processes forproducing thermo-expansive microcapsules are usually employed. In thoseprocesses, inorganic microparticles such as colloidal silica, colloidalcalcium carbonate, magnesium hydroxide, calcium phosphate, aluminumhydroxide and alumina, are employed as the stabilizers for aqueousdispersion. In addition, polymeric dispersion stabilizers, such as thecondensation products of diethanolamine and aliphatic dicarboxylic acid,polyvinyl pyrolidone, methyl cellulose, polyethylene oxide and polyvinylalcohol; and various emulsifiers including cationic surfactants, such asalkyltrimethyl ammonium chloride and dialkyldimethylammonium chloride,anionic surfactants, such as sodium alkyl sulfate, and amphotericsurfactants, such as alkyldimethyl aminoacetic acid betaine andalkyldihydroxyethyl aminoacetic acid betaine are employed as dispersionstabilizers.

The preferable thermo-expansive microspheres of the present inventionhave average particle sizes ranging from 1 to 100 μm and particle sizedistribution with 30% or less of coefficient of variation, CV. Theaverage particle size of the thermo-expansive microspheres of thepresent invention can be controlled over broad range and designed freelyaccording to their end uses. The coefficient of variation, CV, iscalculated by the following formula:CV=(S/<X>)×100(%)  (1)S={Σ^(a) _(i=1)(Xi−<X>)²/(n−1)}^(1/2)  (2)where S is the standard deviation of particle size, <X> is an averageparticle size, Xi is the size of a particle of the i-th order, and n isthe number of particles.

For producing expanded hollow microspheres from the thermo-expansivemicrospheres of the present invention, it is preferable to heat themicrospheres at a temperature higher than the softening point of thethermoplastic resin of the shell to expand the microspheres into avolume with an expansion ratio of 10 or more. With this treatment,expanded microspheres having a specific gravity of 0.1 or lower andparticle size distribution with 30% or lower coefficient of variation,CV, are produced. Particle size distribution with a coefficient ofvariation or CV greater than 30% is not preferable, because it mayresult in variable expanding performance of thermo-expansivemicrospheres. In addition, thermo-expansive microspheres withexcessively varied particle sizes will adversely affect on the surfacefinish of products in which the thermo-expansive microspheres areblended or mixed.

The average particle sizes of the thermo-expansive microspheres andexpanded hollow microspheres of the present invention were determined bya laser diffraction particle size distribution tester (Heros & Rodos,manufactured by Sympatec Co., Ltd.).

The true specific gravity of the thermo-expansive microspheres of thepresent invention was determined by a liquid substitution method withisopropyl alcohol.

The expansion ratio of said thermo-expansive microspheres was determinedby dividing the true specific gravity of unexpanded thermo-expansivemicrospheres with the true specific gravity of expanded hollowmicrospheres, which was expanded by heating thermo-expansivemicrospheres in a Perfect Oven manufactured by Tabai Espec Co., Ltd. ata predetermined temperature (expanding temperature) for two minutes.

A fine-particle coating agent for the thermo-expansive microspheres ofthe present invention having smaller particle sizes than that of thethermo-expansive microspheres, preferably smaller than one tenth of theparticle size of the thermo-expansive microspheres, are selected amongorganic coating agents or inorganic coating agents according to thepurpose of their application, such as improving dispersibility inmaterials or flowability of said microspheres, and preventing the fusionof said microspheres in heating and expanding. The preferable ratio ofsaid fine-particle coating agent adsorbed to thermo-expansivemicrospheres ranges from 0.1 to 95 weight percent, more preferably from0.5 to 60 weight percent, and most preferably from 5 to 50 weightpercent. A ratio beyond the range is not preferable, because a ratiolower than 0.1 weight percent cannot attain said property, and a ratiogreater than 95 weight percent increases the true specific gravity ofmicrospheres beyond a preferable range.

The examples of the organic coating agent are metal soaps, such asmagnesium stearate, calcium stearate, zinc stearate, barium stearate,and lithium stearate; resin powders, such as polytetrafluoroethylenebeads and polymethyl methacrylate beads; and polyamide fiber.

The examples of the inorganic coating agent are silica, alumina, mica,talc, isinglass, calcium carbonate, calcium hydroxide, calciumphosphate, magnesium hydroxide, magnesium phosphate, barium sulfate,titanium dioxide, zinc oxide, ceramic beads, glass beads, crystal beads,carbon black, and molybdenum disulfide. Those organic or inorganiccoating agents can be used in a form of mixture.

For preventing the fusion of microspheres mentioned above, an organiccompound having a melting point of 90° C. or higher, preferably 130° C.or higher, or an inorganic compound of which crystal is formed intolayer lattice is preferable.

Ordinary powder mixers, which can oscillate and agitate powder, can beemployed for mixing thermo-expansive microspheres and a fine-particlecoating agent. Specifically, powder mixers which can oscillate andagitate or agitate powder, such as ribbon-type mixers and vertical screwmixers, can be employed. Recently, highly efficient multi-functionalpowder mixers manufactured by combining several agitation devices, suchas Super Mixer (manufactured by Kawata MFG Co., Ltd.), High-Speed Mixer(manufactured by Fukae Co., Ltd.) and New-Gra Machine (manufactured bySeishin Enterprise Co., Ltd.), have been introduced and thus they areemployable. In addition, a simple device consisting of a vessel andpaddle blades is applicable.

Said fine-particle coating agent sticks on the surface ofthermo-expansive microspheres.

The thermo-expansive microspheres of the present invention can beprocessed into lightweight foamed compositions by blending them withresins, such as rubber, thermoplastic resins, and thermo-setting resins,and by heating.

Expanded hollow microspheres produced from the thermoplasticmicrospheres of the present invention can be processed into lightweightresin compositions by blending them with resins, such as rubber,thermoplastic resins, and thermo-setting resins. The examples ofapplicable resins are SBS (styrene-butadiene-styrene block copolymer),PVC (polyvinyl chloride), PP (polypropylene), PE (polyethylene), PU(polyurethane), PS (polystyrene), natural rubber, acrylic resin, epoxyresin, and silicone resin, though the applicable resins are notrestricted within the scope of those examples.

The preferable ratio of thermo-expansive microspheres and expandedhollow microspheres in a resultant composition ranges from 0.5 to 50weight percent, more preferably from 1.0 to 30 weight percent.

The advantages of the thermo-expansive microspheres of the presentinvention are processability into expanded hollow microspheres withalmost no emission of fluorine-containing compounds; much narrowerparticle size distribution range than the ranges of otherthermo-expansive microspheres in which aliphatic fluorocarbons or fluorohydrocarbons are encapsulated; and superior expanding performance.Another advantage of the thermo-expansive microspheres in which suchblowing agents are encapsulated is their applicability asflame-retardant or flame-resistant materials having low environmentalloading.

The retaining ratio, or percent, of a blowing agent encapsulated inthermo-expansive microsp heres is defined as G₂/G₁×100; where G₁ is theweight of a blowing agent encapsulated in thermo-expansive microspheresbefore expansion and G₂ is the weight of a blowing agent encapsulated inthermo-expansive microspheres after expansion. A fluorine compoundhaving ether linkage is encapsulated as a blowing agent in thethermo-expansive microspheres of the present invention, and theretaining ratio of the blowing agent should be 90 percent or more,preferably 95 percent or more, more preferably 97 percent or more. Aretaining ratio lower than 90 percent may cause uneven property ofexpanded microspheres because considerable ratio of a blowing agent isreleased through shell polymer in thermo-expanding process ofthermo-expansive microspheres. In addition, it gives adverse effect onthe stability of expanded microspheres during storage.

The thermo-expansive microspheres and expanded hollow microspheres ofthe present invention are applicable to various end uses. Unexpandedthermo-expansive microspheres are applied as the fillers of automobilepaints and the foaming agents of foaming inks to be applied to wallpapers and decoration for apparels owing to their thermo-expansiveperformance. Furthermore, unexpanded thermo-expansive microspheres canbe used as foaming agents for imparting lightweight, porous, cushioningand thermo-insulating property in a process where the microspheres areblended with thermoplastic resins or thermo-setting resins and heated toexpand the microspheres at a temperature higher than a point at whichthe microspheres start to expand.

Expanded thermo-expansive microspheres can be applied as lightweightfillers for paints, putty, composite materials, paper, and insulatingmaterials, and as volume-retaining materials for pressure vessels, owingto their low density and filling effect. As described above, thethermo-expansive microspheres of the present invention can be applied tothe same end uses as those for conventional thermo-expansivemicrospheres.

Further, the present invention can be applied to flame-resistant paintsand insulating materials. In flame-resistant paints, the above-mentionedthermo-expansive microspheres can be used as flame-retardant orflame-resistant fillers.

EXAMPLES

The present invention is described precisely with the following examplesand comparative examples.

Example 1

A water phase was prepared by adding 150 g of salt, 3.0 g of an adipicacid-diethanolamine condensate, and 20 g of colloidal silica (20%concentration) in 500 g of deionized water and by homogenizing themixture with agitation.

An oil phase was prepared by mixing 200 g of acrylonitrile, 70 g ofmethacrylonitrile, 5.0 g of methyl methacrylate, 1.2 g of ethyleneglycol dimethacrylate, 2.0 g of azobisisobutyronitrile, and 150 g ofmethylperfluorobutyl ether, and by dissolving the components withagitation.

Then the water phase and oil phase were mixed preliminarily with ahomogenizer at 3,000 rpm for 2 minutes, and then agitated at 10,000 rpmfor 2 minutes to be prepared into suspension. Then the suspension wastransferred in a reactor, purged with nitrogen, and reacted at 61° C.for 20 hours under agitation. The reaction product was filtered anddried. The resultant microspheres had an average particle size of 30 μmwith CV or coefficient of variation of 27%. The true specific gravity ofthe thermo-expansive microspheres was determined to be 1.23. The ratioof the blowing agent encapsulated in the thermo-expansive microsphereswas determined to be 33.8 weight percent. The microspheres did not burnwhen a source of ignition, flame from a lighter, was brought close tothem. The angle of repose of the microspheres, which indicates thedegree of flowability of powder, was determined with a Powder Tester(PT-N, manufactured by Hosokawa Micron Corporation), and the result was43 degrees.

The resultant thermo-expansive microspheres were heated at 160° C. for 2minutes to be processed into expanded hollow microspheres. The expandedhollow microspheres had an average particle size of 120 μm with CV orcoefficient of variation of 27%. The true specific gravity of themicrospheres was 0.020, with an expansion ratio of 61. Subsequently theratio of the blowing agent encapsulated in the expanded hollowmicrospheres was determined to be 33.2 weight percent. The expandedhollow microspheres did not burn when a source of ignition was broughtclose to them.

Example 2

The thermo-expansive microspheres produced in Example 1 and titaniumdioxide, having an average particle size of 15 nm, were mixed in 6:4weight ratio and agitated uniformly with a Super Mixer (manufactured byKawata MFG Co., Ltd.) to produce thermo-expansive microspheres having asurface coated with titanium dioxide. Their average particle size was 30μm with CV or coefficient of variation of 27%. The angle of repose ofthe microspheres was determined to be 0 degree, exhibiting excellentflowability.

Example 3

Thermo-expansive microspheres were produced in the same manner as inExample 1 except that an inline homogenizer was employed instead of thehomogenizer employed in Example. The resultant thermo-expansivemicrospheres had an average particle size of 31 μm with CV orcoefficient of variation of 15% and a true specific gravity of 1.20, andthe ratio of the blowing agent was 33.2 weight percent. Thethermo-expansive microspheres did not burn when a source of ignition wasbrought close to them.

The microspheres were heated at 160° C. for 2 minutes in the same manneras in Example 1 to be processed into expanded hollow microspheres. Theexpanded hollow microspheres had an average particle size of 120 μm withCV or coefficient of variation of 16%, a true specific gravity of 0.021,and an expansion ratio of 57.

Subsequently the ratio of the blowing agent encapsulated in the expandedhollow microspheres was determined to be 31.9 weight percent. Theexpanded hollow microspheres did not burn when a source of ignition wasbrought close to them.

Comparative Example 1

Thermo-expansive microspheres were produced in the same manner as inExample 1 except that 150 g of methylperfluorobutyl ether was replacedby 65 g of isohexane.

The resultant thermo-expansive microspheres had an average particle sizeof 31 μm with CV or coefficient of variation of 44% and a true specificgravity of 1.02, and the ratio of the blowing agent was 17.5 weightpercent. The thermo-expansive microspheres inflamed when a source ofignition was brought close to them.

The microspheres were heated at 160° C. for 2 minutes in the same manneras in Example 1 to be processed into expanded hollow microspheres. Theexpanded hollow microspheres had an average particle size of 110 μm withCV or coefficient of variation of 42%, a true specific gravity of 0.019,and an expansion ratio of 53.

Subsequently the ratio of the blowing agent encapsulated in the expandedhollow microspheres was determined to be 14.6 weight percent. Theexpanded hollow microspheres inflamed when a source of ignition wasbrought close to them.

Comparative Example 2

Thermo-expansive microspheres were produced in the same manner as inExample 1 except that 150 g of methylperfluorobutyl ether was replacedby 161.5 g of perfluorocarbon (C₆F₁₄).

The resultant thermo-expansive microspheres had an average particle sizeof 30 μm with CV or coefficient of variation of 45% and a true specificgravity of 1.20, and the ratio of the blowing agent was 27.5 weightpercent. The thermo-expansive microspheres did not burn when a source ofignition was brought close to them.

The microspheres were heated at 160° C. for 2 minutes in the same manneras in Example 1 to be processed into expanded hollow microspheres. Theexpanded hollow microspheres had an average particle size of 110 μm withCV or coefficient of variation of 46%, a true specific gravity of 0.028,and an expansion ratio of 43.

Subsequently the ratio of the blowing agent encapsulated in the expandedhollow microspheres was determined to be 24.3 weight percent. Theexpanded hollow microspheres did not burn when a source of ignition wasbrought close to them.

Comparative Example 3

Thermo-expansive microspheres were produced in the same manner as inComparative Example 2 except that 7.0 g of dimethyl adipate was added tothe oil phase.

The resultant thermo-expansive microspheres had an average particle sizeof 21 μm with CV or coefficient of variation of 48% and a true specificgravity of 1.19, and the ratio of the blowing agent was 20.5 weightpercent. The thermo-expansive microspheres did not burn when a source ofignition was brought close to them.

The microspheres were heated at 160° C. for 2 minutes in the same manneras in Example 1 to be processed into expanded hollow microspheres. Theexpanded hollow microspheres had an average particle size of 70 μm withCV or coefficient of variation of 48%, a true specific gravity of 0.032,and an expansion ratio of 37.

Subsequently the ratio of the blowing agent encapsulated in the expandedhollow microspheres was determined to be 16.3 weight percent. Theexpanded hollow microspheres did not burn when a source of ignition wasbrought close to them.

Comparative Example 4

Thermo-expansive microspheres were produced in the same manner as inComparative Example 3 except that 7.0 g of dimethyl adipate in the oilphase was replaced by 12.7 g of dimethyl octafluoroadipate.

The resultant thermo-expansive microspheres had an average particle sizeof 18 μm with CV or coefficient of variation of 42% and a true specificgravity of 1.21, and the ratio of the blowing agent was 24.5 weightpercent. The thermo-expansive microspheres did not burn when a source ofignition was brought close to them.

The microspheres were heated at 160° C. for 2 minutes in the same manneras in Example 1 to be processed into expanded hollow microspheres. Theexpanded hollow microspheres had an average particle size of 38 μm withCV or coefficient of variation of 41%, a true specific gravity of 0.172,and an expansion ratio of 7.

Subsequently the ratio of the blowing agent encapsulated in the expandedhollow microspheres was determined to be 16.3 weight percent. Theexpanded hollow microspheres did not burn when a source of ignition wasbrought close to them.

Example 4

Thermo-expansive microspheres were produced in the same manner as inExample 1 except that the oil phase was prepared by mixing 200 g ofacrylonitrile, 75 g of methyl methacrylate, 1.2 g of ethyleneglycoldimethacrylate, 2.0 g of azobisisobutyronitrile, 100 g ofmethylperfluorobutyl ether, and 20 g of isobutane, and by agitating todissolve those components.

The resultant thermo-expansive microspheres had an average particle sizeof 22 μm with CV or coefficient of variation of 25% and a true specificgravity of 1.16, and the ratio of the blowing agent was 28.9 weightpercent. The thermo-expansive microspheres did not burn when a source ofignition was brought close to them.

The microspheres were heated at 140° C. for 2 minutes to be processedinto expanded hollow microspheres. The expanded hollow microspheres hadan average particle size of 88 μm with CV or coefficient of variation of24%, a true specific gravity of 0.019, and an expansion ratio of 63.

Subsequently the ratio of the blowing agent encapsulated in the expandedhollow microspheres was determined to be 26.3 weight percent. Theexpanded hollow microspheres did not burn when a source of ignition wasbrought close to them.

Comparative Example 5

Thermo-expansive microspheres were produced in the same manner as inExample 4, except that 100 g of methylperfluorobutyl ether was replacedby 41.0 g of isohexane.

The resultant thermo-expansive microspheres had an average particle sizeof 21 μm with CV or coefficient of variation of 38% and a true specificgravity of 1.03, and the ratio of the blowing agent was 15.2 weightpercent. The thermo-expansive microspheres inflamed when a source ofignition was brought close to them.

The microspheres were heated at 140° C. for 2 minutes in the same manneras in Example 4 to be processed into expanded hollow microspheres. Theexpanded hollow microspheres had an average particle size of 78 μm withCV or coefficient of variation of 39%, a true specific gravity of 0.021,and an expansion ratio of 49.

Subsequently the ratio of the blowing agent encapsulated in the expandedhollow microspheres was determined to be 11.3 weight percent. Theexpanded hollow microspheres inflamed when a source of ignition wasbrought close to them.

Example 5

Thermo-expansive microspheres were produced in the same manner as inExample 1 except that the oil phase was prepared by mixing 150 g ofacrylonitrile, 120 g of vinylidene chloride, 5.0 g of methylmethacrylate, 0.8 g of trimethylolpropane trimethacrylate, 1.0 g ofdiisopropyl peroxidicarbonate, 90 g of methylperfluorobutyl ether, and20 g of isobutane, and agitating to dissolve those components.

The resultant thermo-expansive microspheres had an average particle sizeof 15 μm with CV or coefficient of variation of 24% and a true specificgravity of 1.33, and the ratio of the blowing agent was 25.9 weightpercent The thermo-expansive microspheres did not burn when a source ofignition was brought close to them.

The resultant microspheres were heated at 120° C. for 2 minutes to beprocessed into expanded hollow microspheres. The expanded hollowmicrospheres had an average particle size of 63 μm with CV orcoefficient of variation of 24%, a true specific gravity of 0.018, andan expansion ratio of 72.

Subsequently the ratio of the blowing agent encapsulated in the expandedhollow microspheres was determined to be 24.7 weight percent. Theexpanded hollow microspheres did not burn when a source of ignition wasbrought close to them.

Comparative Example 6

Thermo-expansive microspheres were produced in the same manner as inExample 3, except that 90 g of methylperfluorobutyl ether was replacedby 36.9 g of normal pentane.

The resultant thermo-expansive microspheres had an average particle sizeof 13 μm with CV or coefficient of variation of 38% and a true specificgravity of 1.26, and the ratio of the blowing agent was 14.2 weightpercent. The thermo-expansive microspheres inflamed when a source ofignition was brought close to them.

The microspheres were heated at 120° C. for 2 minutes in the same manneras in Example 5 to be processed into expanded hollow microspheres. Theexpanded hollow microspheres had an average particle size of 46.4 μmwith CV or coefficient of variation of 39%, a true specific gravity of0.029, and an expansion ratio of 43.

Subsequently the ratio of the blowing agent encapsulated in the expandedhollow microspheres was determined to be 9.3 weight percent. Theexpanded hollow microspheres inflamed when a source of ignition wasbrought close to them.

Example 6

Two weight percent of the thermo-expansive microspheres produced inExample 1 was moistened with 2 weight percent of a process oil, mixedwith 96 weight percent of SBS (styrene-butadiene-styrene blockcopolymer, having a specific gravity of 0.9), and knead with biaxialrolls at 80° C. to be processed into rubber sheet. Then the rubber sheetwas heated at 160° C. for 10 minutes with a hot pressing device to beprocessed into foamed rubber sheet. The result is shown in Table 1.

Comparative Example 7

Foamed rubber sheet was produced in the same manner as in Example 6,except that the thermo-expansive microspheres produced in Example 1 wasreplaced by the thermo-expansive microspheres produced in ComparativeExample 4. The result is shown in Table 1.

TABLE 1 Surface finish of foamed rubber Specific gravity of sheet *1foamed rubber sheet *2 Example 6 good 0.53 Comparative poor 0.85 Example7 *1 The surface roughness of foamed rubber sheet was visuallyinspected. *2 determined with a high-precision Electronic Densimeter(SD-200L, produced by Mirage Trading Co., Ltd.)

The thermo-expansive microspheres of the present invention have a narrowrange of particle size distribution and superior expanding performance.Therefore the foamed rubber sheet produced with the thermo-expansivemicrospheres has good surface finish and light weight owing to theeffective function of the thermo-expansive microspheres.

Example 7

Five weight percent of expanded hollow microspheres (with an averageparticle size of 120 μm, CV or coefficient of variation of 27%, and atrue specific gravity of 0.020) produced by heating the thermo-expansivemicrospheres of Example 1 was mixed with 95 weight percent of a PVC-solpaint (with a specific gravity of 1.4), and painted on a substrate. Thenthe painted substrate was heated for gelling the mixed paint in aPerfect Oven at 160° C. for 30 minutes to process the coating into asheet. The result is shown in Table 2.

Comparative Example 8

A sheet was produced in the same manner as in Example 7, except thatexpanded hollow microspheres (with an average particle size of 38 μm, CVor coefficient of variation of 41%, and a true specific gravity of0.172) produced by heating the thermo-expansive microspheres ofComparative Example 4 instead of the thermo-expansive microspheres ofExample 1 were employed. The result is shown in Table 2.

TABLE 2 Surface finish of Specific gravity of PVC sheet *1 PVC sheet *2Example 7 good 0.32 Comparative poor 0.94 Example 8 *1 The surfaceroughness of PVC sheet was visually inspected. *2 determined with ahigh-precision Electronic Densimeter (SD-200L, produced by MirageTrading Co., Ltd.)

Example 8

A balloon was filled with 50 g of expanded hollow microspheres (with anaverage particle size of 120 μm, CV or coefficient of variation of 27%,and a true specific gravity of 0.020) produced by expanding thethermo-expansive microspheres of Example 1, instead of the air, and wasexpanded to a volume of 4 liter. The balloon was stored at 50° C. for 1month, but the volume did not decrease.

Example 9

The thermo-expansive microspheres produced in Example 1 and magnesiumstearate having an average particle size of 2 μm and a melting point of132° C. were mixed in 9:1 weight ratio and agitated uniformly with aSuper Mixer (manufactured by Kawata MFG Co., Ltd.) to be processed intothermo-expansive microspheres having a surface coated with magnesiumstearate. They had an average particle size of 30 μm with CV orcoefficient of variation of 27%. The ratio of the encapsulated blowingagent was 30.7 weight percent.

Then the microspheres were heated at 160° C. for 2 minutes in the samemanner as in Example 1 to be processed into expanded hollowmicrospheres. The expanded hollow microspheres had an average particlesize of 113 μm with CV or coefficient of variation of 28%, a truespecific gravity of 0.024, the ratio of the encapsulated blowing agentwas 30.2 weight percent, and the fusion of the expanded hollowmicrospheres are not observed. The expanded hollow microspheres did notburn when a source of ignition, flame from a lighter, was brought closeto them.

Example 10

Thermo-expansive microspheres and expanded hollow microspheres thereofhaving surface coated with acetylene black were produced in the samemanner as in Example 9, except that the magnesium stearate was replacedby acetylene black having an average particle size of 42 nm. Theresultant thermo-expansive microspheres had an average particle size of30 μm with CV or coefficient of variation of 27%. The ratio of theencapsulated blowing agent was 30.6 weight percent.

The resultant expanded hollow microspheres had an average particle sizeof 118 μm with CV or coefficient of variation of 28%, and contained nofused microspheres. The resultant expanded hollow microspheres had atrue specific gravity of 0.022, the ratio of the encapsulated blowingagent was 30.4 weight percent, and the fusion of the expanded hollowmicrospheres are not observed.

1. Thermo-expansive microspheres comprising a shell of thermoplasticresin and a blowing agent encapsulated in the shell; said blowing agentbeing a fluorine-containing compound having ether linkage, being free ofchlorine and bromine atoms, and gasifying at a temperature not higherthan the softening point of said thermoplastic resin, wherein thefluorine-containing compound includes at least one member selected fromthe group consisting of C₃F₇OCH₃, C₄F₉OCH₃, C₄F₉OC₂H₅, and C₇F₁₅OC₂H₅;the thermo-expansive microspheres have a CV, or coefficient ofvariation, of particle size distribution being 30% or less and saidthermoplastic resin comprises a polymer of monomeric mixture containing0.01 to 0.43 weight percent of a polymerizable monomer having at leasttwo polymerizable double bonds.
 2. The thermo-expansive microspheres ofclaim 1, wherein the monomeric mixture further contains 80 weightpercent or more of a nitrile monomer.
 3. The thermo-expansivemicrospheres of claim 1 or claim 2, wherein said thermo-expansivemicrospheres contain 2 to 85 weight percent of said blowing agent. 4.The thermo-expansive microspheres of claim 1, having a retaining ratioof blowing agent encapsulated being 90% or more.
 5. The thermo-expansivemicrospheres of claim 1, wherein the fluorine-containing compoundincludes at least one compound selected from the group consistingC₃F₇OCH₃ and C₇F₁₅OC₂H₅.
 6. The thermo-expansive microspheres of claim1, wherein the polymerizable monomer having at least two polymerizabledouble bonds includes at least one member selected from the groupconsisting of aromatic divinyl compounds, ethylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycoldi(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,9-nonanedioldi(meth)acrylate, 1,10-decanediol di(meth)acrylate, PEG (200)di(meth)acrylate, PEG (400) di(meth)acrylate, PEG (600)di(meth)acrylate, neopentylglycol di(meth)acrylate, 1,4-butanedioldimethacrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanedioldi(meth)acrylate, glycerin dimethacrylate, dimethylol tricyclodecanediacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, hydroxypivalicacid neopentylglycol diacrylate, and 2-butyl-2-ethyl-1,3-propanedioldiacrylate.
 7. The thermo-expansive microspheres of claim 1, wherein thesurface of said microspheres is coated with 0.1 to 95 weight percent ofa fine-particle coating agent having a primary particle size not greaterthan one tenth of the particle size of said thermo-expansivemicrospheres.
 8. The thermo-expansive microspheres of claim 1, whereinthe surface of said microspheres is coated with 0.1 to 95 weight percentof a fine-particle coating agent comprising at least one selected from agroup consisting of organic compounds having a melting point of 90° C.or higher and inorganic compounds formed into a layer lattice. 9.Expanded hollow microspheres produced by heating the thermo-expansivemicrospheres of claim 1 at a temperature not lower than the softeningpoint of their thermoplastic resinous shell to expand to a volume of 10or more of expansion ratio, being characterized by their true specificgravity of 0.1 or lower and particle size distribution with a CV, orcoefficient of variation, of 30% or less.
 10. Volume-retaining materialproduced by filling pressure vessel with the expanded hollowmicrospheres of claim
 9. 11. The thermo-expansive microspheres of claim1, wherein said thermo-expansive microspheres contain 30 to 50 weightpercent of said blowing agent.
 12. Volume-retaining material produced byfilling pressure vessel with expanded hollow microspheres which areproduced by heating thermo-expansive microspheres at a temperature notlower than the softening point of their thermoplastic resinous shell toexpand to a volume of 10 or more of expansion ratio, and which arecharacterized by their true specific gravity of 0.1 or lower andparticle size distribution with a CV, or coefficient of variation, of30% or less, wherein the thermo-expansive microspheres comprise a shellof thermoplastic resin and a blowing agent encapsulated in the shell,and have a retaining ratio of blowing agent encapsulated being 90% ormore; said blowing agent including at least one member selected from thegroup consisting of C₃F₇OCH₃ and C₇F₁₅OC₂H₅, and gasifying at atemperature not higher than the softening point of said thermoplasticresin; the surface of said microspheres is coated with 0.1 to 95 weightpercent of a fine-particle coating agent comprising at least oneselected from the group consisting of organic compounds having a meltingpoint of 90° C. or higher and inorganic compounds formed into layerlattice; and said thermoplastic resin comprises a polymer of monomericmixture containing 0.01 to 0.43 weight percent of a polymerizablemonomer having at least two polymerizable double bonds.